This invention relates to a fluid filter. More particularly, the invention is directed to a filter designed for installation in an annular groove.
In certain applications, a fluid filter must meet stringent performance and durability requirements. One such application is a supply filter for a variable bleed solenoid used for controlling line pressure in a vehicle's automatic transmission. The solenoid is susceptible to contamination in its fluid supply. Due to the internal design of the variable bleed solenoid and the small orifices contained therein, contamination migrating inside the device can affect its performance. The filter, when installed on the variable bleed solenoid, must adequately remove contaminates from the supply fluid so that the solenoid continues to operate properly. In addition, the filter must be able to withstand relatively high temperatures, pressures and vibration levels present in the transmission environment. It is imperative that the filter remains intact and does not become loose or deformed under the environmental conditions present.
It is conventional to use a supply filter designed for installation in an annular groove around the housing of the variable bleed solenoid. A typical design for a solenoid filter is shown in FIG. 5. The filter is molded in a cylindrical configuration and split to permit assembly into an annular groove of a solenoid housing. The design contains a polymeric frame and ribs to add rigidity to the filter. Designed in rigidity is directed to preventing fluid contamination from entering the solenoid around the edge of the filter.
The filter element is typically comprised of a screen-like material onto which the plastic frame is integrally molded. This type of design, which requires the part to be molded in an annular configuration incorporating ribs and a frame has proven difficult to manufacture. The difficulties associated with producing a filter of this design include accurately positioning the filter element material within the annular mold. In addition, malformation of the molded features of the filter can occur due to the need for plastic to flow about the filter element to form the frame and ribs. Movement of the filter element during the molding process can contribute to malformation problems. Another potential problem is formation of the frame and ribs with a missing filter element.
Because of the difficulties associated with producing a filter according to prior practice, supply filters typically require 100 percent inspection to ensure proper filter element positioning and presence. The cost of a filter according to this design is driven up due to the complexity of the manufacturing requirements.
Another drawback associated with a filter according to the prior art design as shown in FIG. 5 is that the frame and rib construction obstructs filter element area that would otherwise be available to remove contaminants from the fluid supplied to the solenoid. Accordingly, problems associated with filter elements used to remove contaminants from the supply fluid to a variable bleed solenoid exist. It would be preferable if a filter was designed for ease of manufacturing while still providing adequate filtering for the contaminant sensitive application requirements.